The black level in the generated image can be reduced by such an arrangement. However, the problem arises that an absolutely precise pixel-accurate imaging is almost impossible to achieve in practice. For example, with a desired, pixel-accurate imaging, this leads to the modulator pixels of the second modulator which are to represent a predefined brightness in the image and which are adjacent to modulator pixels which are to represent black and therefore e.g. are not illuminated, being illuminated with less intensity than modulator pixels which are surrounded only by modulator pixels which are also to represent bright picture elements. This leads to undesired brightness fluctuations in such areas.
This effect may be wavelength-dependent due to chromatic errors in the imaging optics with the result that, when presenting multicoloured images, if colour subframes are generated in such rapid succession that the colour subframes can be detected by the user only in temporal superimposition, but not individually, the colour portions of the individual colour images fluctuate in an undesired manner, which leads to colour aberrations in the image to be projected. The same problem occurs if the colour subframes are generated simultaneously with several modulators and imaged onto the second modulator.
According to the invention a projector for projecting an image is to be provided with which these problems can be solved. Furthermore, a corresponding method for projecting an image is to be provided.
As, with the projector according to the invention, according to a first alternative precisely one image pixel is allocated to each illumination pixel on the basis of the imaging optics, and the illumination control data are generated such that they have the on-value for each illumination pixel which is allocated to an image pixel which is, according to the image data, to represent a brightness value lying above a predetermined threshold value in the image, and the off-value for all other illumination pixels, except that the illumination control data have the on-value for at least one of the other illumination pixels whose allocated image pixel is no more than a predetermined number of pixels away from an image pixel which is, according to the image data, to represent a brightness value lying above the threshold value, bright edge image pixels with which bright edge image spots adjacent to dark image spots are to be generated in the image to be projected are illuminated in the same way as bright image pixels which are surrounded exclusively by bright image pixels. Thus a very uniform illumination of the edge image pixels is also achieved, whereby the problems described at the start can be overcome.
According to a second alternative of the projector according to the invention several image pixels are allocated to each illumination pixel. As the illumination control data have the on-value for each illumination pixel which is allocated to at least one image pixel which is, according to the image data, to represent a brightness value lying above a predetermined threshold value in the image and the off-value for all other illumination pixels, except that the illumination control data have the on-value for at least one of the other illumination pixels at least one of whose allocated image pixels is no more than a predetermined number of pixels away from an image pixel which is, according to the image data, to represent a brightness value lying above the threshold value, bright edge image pixels with which bright edge image spots adjacent to dark image spots are to be generated in the image to be projected are illuminated in the same way as bright image pixels which are surrounded exclusively by bright image pixels. Thus a very uniform illumination of the edge image pixels is also achieved, whereby the problems described at the start can be overcome.
In particular the control unit can generate the illumination control data such that they have the on-value for each of the other illumination pixels whose allocated image pixel or at least one of whose allocated image pixels is no more than a predetermined number of pixels away from an image pixel which is, according to the image data, to represent a brightness value lying above the threshold value. Thus it can be ensured that all edge image pixels are illuminated in the same manner.
The predetermined number of pixels can be 0, with the result that the illumination control data have the on-value for every other illumination pixel whose allocated image pixel or at least one of whose allocated image pixels is (are) directly adjacent to an image pixel which is, according to the image data, to represent a brightness value lying above a predetermined threshold value. If the predetermined number of pixels is 0 only the black image pixels which are directly adjacent to an image pixel which is, according to the image data, to represent a brightness value lying above the predetermined threshold value are illuminated.
If not only directly adjacent black image pixels but also black image pixels further away are also to be illuminated, the number of pixels can have a corresponding higher value than 0.
Thus the predetermined number of pixels can be 1, 2, 3 or have another value. A value greater than or equal to 1 can be chosen if e.g. the imaging optics generate undesired pixel shifts. Account can thereby also be taken of the so-called spatial dithering in which, to improve the image, the control unit also switches to bright image pixels which, according to the image data, are not actually to represent a brightness lying above the predetermined threshold value.
In the projector, the illumination pixels can be switched in each case into a first state in which the light coming from the illumination pixel is imaged onto the allocated image pixel, and into a second state in which no light is imaged from the illumination pixel onto the allocated image pixel, and the image pixels can be switched in each case into a first state in which the light coming from the image pixel is used to generate the image, and into a second state in which no light from the image pixel is used to generate the image. A digital control of the two modulators is thus possible. In particular for example LCD, LCoS modulators or tilting mirror matrices can be used as modulators. The modulators can be reflective or transmissive. The projector according to the invention can contain modulators of the same or different type. In one embodiment it contains modulators of the same type, for example two tilting mirror matrices.
In the illumination control data, the on-value for the illumination pixels can be chosen by the control unit such that each illumination pixel which is allocated to an image pixel which is, according to the image data, to represent a brightness value lying above the predetermined threshold value is always switched into the first state at the times when the allocated image pixel is switched into the first state. Thus it is ensured that the desired brightness value of the image pixel can be achieved, wherein simultaneously a reduction of the black level can be achieved.
The control unit can choose the on-value for the illumination pixels in the illumination control data such that each illumination pixel which is allocated to an image pixel which is, according to the image data, to represent a brightness value which lies above the predetermined threshold value and below a predetermined maximum value is at least sometimes also switched into the second state during the times when the allocated image pixel is switched into the second state. Thus an illumination matched to the switching states of the image pixels is made possible, whereby disruptive background brightness can be reduced.
Furthermore, in the illumination control data, the on-value for the other illumination pixels can be chosen such that the other illumination pixels are always switched into the first state at the times when at least one of the image pixels no more than the predetermined number of pixels away from the allocated image pixel is switched into the first state. The on-value for the other illumination pixels can in particular be chosen such that every other illumination pixel whose allocated image pixel is no more than the predetermined number of pixels away from at least one other image pixel which is to represent a brightness value which lies above the predetermined threshold value and below a maximum value is also at least sometimes switched into the second state when the at least one other image pixel is switched into the second state. Thus the illumination matched to the switching times is also carried out for the other image pixels to which the on-value is allocated. This leads to a further reduction in undesired background brightness.
In the projector, the control unit can also choose the on-value for the illumination pixels in the illumination control data such that each illumination pixel which is allocated to an image pixel which is, according to the image data, to represent a brightness value lying above the predetermined threshold value is always switched into the first state precisely only at the times when the allocated image pixel is switched into the first state. An illumination completely matched to the times of the first state is thus achieved.
In particular, the on-value for the other illumination pixels can also be chosen such that the other illumination pixels are always switched into the first state precisely only at the times when at least one of the image pixels no more than the predetermined number of pixels away from the allocated image pixel is switched into the first state.
The illumination and image control data can in each case be pulse-width modulated control data. In particular the control data for each illumination and image pixel can in each case contain a binary data value of equal bit depth, wherein the on-value for each illumination pixel which is allocated to an image pixel which is, according to the image data, to represent a brightness value lying above the predetermined threshold value in the image is chosen such that at least the same bits are set as in the binary data value of the allocated image pixel. An illumination of the image pixel matched to the bit-switching times can thus be achieved.
In particular the on-value for the illumination pixels can be chosen such that all bits are set which are set in the binary data value of the allocated image pixel and in the binary data values of all of the image pixels that are no more than the predetermined number of pixels away from the allocated image pixel.
The object is also achieved by a projector for projecting an image according to claim 27. With this projector the control unit generates the illumination control data such that they have the on-value for each illumination pixel which is allocated to at least one image pixel which is, according to the image data, to represent a brightness value lying above the predetermined threshold value in the image, and the off-value for all other illumination pixels, with the result that with these illumination control data a uniform illumination of edge image pixels is likewise also achieved as each (edge) image pixel is illuminated by the several allocated illumination pixels.
Advantageous versions of the projectors according to the invention are given in the dependent claims.
The illumination modulator and/or the image modulator can in particular have n×m pixels.
The predetermined threshold value is preferably chosen such that the lowest still representable brightness in the image already lies above the threshold value. Thus it is advantageously achieved that the illumination pixels can have the off-value only for image pixels which are to represent a black image spot.
The projector according to the invention can in particular be designed as a projector for applications in a planetarium such that the image to be projected is projected onto a curved projection surface. The curved projection surface can be part of a planetarium dome. In this design projection takes place usually in the dark, with the result that the achieved reduction in black level brings with it a clear improvement in the image.
The projector can furthermore be designed as a projector for front projection or as a projector for rear projection. The projection surface can be a constituent of the projector.
The imaging optics can be designed as 1:1 imaging optics, as enlarging or reducing imaging optics. The design as enlarging or reducing imaging optics is chosen e.g. if the two modulators are of different sizes. It is essential in particular that the desired allocation of the illumination and image pixels is realized.
Furthermore, a method according to claims 14 and 33 is provided. Advantageous versions of the method are given in the dependent method claims.
It is understood that the features named above and still to be explained below can be used not only in the given combinations, but also in other combinations or alone, without departing from the framework of the present invention.